1. Field of the Invention
Apparatuses and methods consistent with the present invention relate to a flat-plate multiple input and multiple output (MIMO) array antenna, and more particularly, to a flat-plate MIMO array antenna that is formed on a substrate in a shape of a flat plate and has an isolation element for preventing interference between antenna elements.
2. Description of the Related Art
An antenna is a component for converting an electric signal into a specified electromagnetic wave to radiate the wave into a free space and vice versa. An effective area in which the antenna radiates or detects the electromagnetic wave is generally referred to as a radiation pattern. A plurality of antenna elements may be arranged in a specific structure to combine radiation pattern and radiation power of each antenna. Accordingly, the overall radiation patterns can be formed to have a sharp shape, and the electromagnetic wave of the antenna can spread out farther. The antenna having such a structure is referred to as an array antenna. The array antenna is used in a MIMO system for implementing multiple input/output operations.
FIG. 1 is a view illustrating an example of a related art flat-plate MIMO array antenna.
The related flat-plate MIMO array antenna shown in FIG. 1 is a 2-channel flat-plate array antenna having two antenna elements 11 and 12 and two feed units 21 and 22. The two antenna elements 11 and 12 are arranged at a half-wave (λ/2) spacing on a substrate 10.
FIG. 2 is a view depicting an S-parameter characteristic to a frequency of the related art flat-plate MIMO array antenna in FIG. 1. In FIG. 2, S11 indicates an S-parameter that is an input reflection coefficient of the first antenna element 11, and S21 indicates an S-parameter that is a mutual coupling of two antenna elements 11 and 12. It will be understood that in the bands of 5.25 GHz and 5.8 GHz, S21 has a value in the range from about −18 dB to about −20 dB.
Since a plurality of antenna elements are used, a problem occurs wherein the mutual coupling resulting from interference between the antenna elements distorts the radiation pattern of the antenna. Accordingly, diverse methods are needed for suppressing the mutual coupling for the related art flat-plate MIMO array antenna.
One such measure for preventing the mutual coupling between the antenna elements in the related art flat-plate MIMO array antenna, involves stacking a 3-dimensional electrical wall between the antenna elements arranged on the substrate, such that a phase difference between the antenna elements becomes 180 degrees or an electrical distance becomes a half wavelength. Accordingly, since the mutual coupling of the antenna elements is suppressed, propagation of the electromagnetic wave radiated from each antenna to other antennas is minimized.
However, since the related art method employs the 3-dimensional configuration, the overall volume of the antenna chip is increased, so that it is difficult to use the antenna in a micro electronic device. Further, there are other drawbacks in that the manufacture itself is difficult, and the integration of the manufactured product is also difficult, causing manufacturing cost to increase significantly.